North Korea, which has sent mixed messages recently, said its threat to cut off dialogue was in response to South Korean media reports this week that Seoul was revising its contingency plans for what it would do if Pyongyang's Korea's leadership falls.
South Korean authorities should bear in mind that they will be excluded from any kind of peace and security talks and negotiations if they don't apologize, the North's official KCNA news agency quoted a military official as saying.
The threat comes a day after North Korea proposed talks with the South to resume joint tourism projects that once gave the cash-short communist state tens of millions of dollars a year.
A holy war for retaliation will be embarked upon to sweep away the base of South Korean authorities who have led and supported this plan, including the presidential Blue House, the North Korean official was quoted as saying.
North Korea has sent mixed signals in the past few weeks, proposing a peace deal to replace the armistice that ended the 1950-53 Korean War while also warning of military moves if it does not get its way.
Analysts said the North's saber rattling was an attempt to increase its bargaining leverage in the event that Pyongyang decides to end its year-long boycott of six-country nuclear disarmament-for-aid talks.
(Reporting by Jon Herskovitz and Rhee So-eui; Editing by Paul Tait)